In order to address the issue of increasing bandwidth requirements demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs.
Certain applications, such as virtual reality (VR) and augmented reality (AR) may demand data rates in the range of several Gigabits per second. Certain wireless communications standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11standard. The IEEE 802.11 standard denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
Amendment 802.11ad to the WLAN standard defines the MAC and PHY layers for very high throughput (VHT) in the 60 GHz range. Operations in the 60 GHz band allow the use of smaller antennas as compared to lower frequencies. However, as compared to operating in lower frequencies, radio waves around the 60 GHz band have high atmospheric attenuation and are subject to higher levels of absorption by atmospheric gases, rain, objects, and the like, resulting in higher free space loss. The higher free space loss can be compensated for by using many small antennas, for example arranged in a phased array.
Using a phased array, multiple antennas may be coordinated to form a coherent beam traveling in a desired direction (or beam), referred to as beamforming. An electrical field may be rotated to change this direction. The resulting transmission is polarized based on the electrical field. A receiver may also include antennas which can adapt to match or adapt to changing transmission polarity.
Some protocols have been devised that use such directional transmissions to passively determine relatively accurate (absolute or relative) positions of devices. In passive positioning, non-access point (AP) stations (STAs) only listen to frame exchanges between APs. By measuring the time these frames are received at the device and a time difference reported by the APs, such STAs can estimate their location. As noted above, however, because transmissions are highly directed in certain bands (e.g., the 60 GHz band) in order to achieve reasonable gain, when the APs communicate between themselves, it is unlikely that the passively listening STAs will receive these transmissions.
Active positioning protocols are based on round trip time (RTT) and angle of arrival (AoA) of transmitted frames. Unfortunately, these methods require separate frame exchanges between stations (STAs). When the number of STAs interested in finding their location becomes high (e.g., some scalable applications may support up to 200 stations per access point AP), the frame exchanges required for measuring the RTT and AoA may take too much air time, thus hampering actual data transmission.